Radio alarm and two-way telephone system



Nov. 18, 1947. 1. F. BYRNEs RADIO ALARM AND TWO-WAY TELEPHONE SYSTEMFiled Feb. 3, 1944 Wfi mw W N .m W. ,F uw.. w 2

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Patented Nov. 18, 1947 RADIO ALARM AND TWO-WAY TELEPHONE SYSTEM IrvingByrnes, Riverdale, N. Y., assignor to Radio Corporation of America, acorporation of Delaware Application February 3, 1944, Serial No. 520,881

7 Claims.

This invention is related to automatic radio alarms and two-waytelephone systems. In radio apparatus for distress signaling and fortwo-way telephoning, it is desirable to have a compact unit on shipboardwhich is adapted for transmission and reception of radio signals andwhich is particularly provided with means for sending and receivingdistress signals.

In marine radio communication systems as used in the past, it has beencustomary to characterize a distress signal by a series of dashes ofdefinite length with intervening spaces of shorter duration. It was thecommon practice to transmit these signals by a hand key. The timing wasdone With the aid of a watch. The receiving apparatus was designed toproduce a response to manually keyed signals despite considerablevariations in the length of the dots and dashes.

Automatic alarm systems such as heretofore used have employed selectivemeans operable in such manner that the alarm is only sounded afterreception of several long dashes, say of approximately four secondsduration each and spaced apart by periods of one second. However, it wasnecessary to adjust the parameters of the selectve means so that thealarm signal would not be sounded in response to static andinterference. Furthermore, it was necessary to adjust the timing of therelay units in the selective means so that there would be no response toextraneous signals brought in on the same carrier wave as that of theestablished distress signal frequency assignment.

There are many limitations and disadvantages in the heretofore usedauto-alarm system. For example, interfering radio signals or static tendto increase the length Vof the dashes sent out from a vessel in distressand also to fill in the space which must be provided between the dashes.Since the auto-alarm signal is transmitted by on-and-off keying, thecarrier and the modula- `tion are both removed during the space intervalbetween dashes. Under these conditions the use of an automatic gaincontrol device is not practical. This in turn requires that thesensitivity of the auto-alarm receiver be adjusted manually, causing itto be "blocked by strong interference or static which may occur afterthe manual adjustment has been made.

In carrying out the instant invention, I propose to overcome thedificulties mentioned in the foregoing. To do this, I propose theadoption of an entirely new form of distress signaling. Instead oftransmitting three or four long dashes spaced apart by short intervalsof silence, I would transmit simultaneously a number of different tonefrequencies which have been predetermined as a suitable combination,such as a musical chord or other mixture of tones for designating thedistress signal. The carrier frequency which is assigned for distresssignaling may then be modulated by this predetermined mixture of tonefrequencies. At the transmitter, therefore, it is necessary to provide aplurality of low frequency oscillators with which to generatesimultaneously the chosen tone frequencies of the distress signal. Thesefrequenciesare to be simultaneously impressed upon the carrier as amodulation. The auto-alarm receiver is, therefore, provided with audiofrequency filters and rectifiers for converting the filtered audiofrequency currents to direct current, which is then used to operate arelay system for producing an audible or visual alarm signal.

In addition to the novel features of the apparatus for sending andreoeiving distress signals, my invention provides means forintercommunication by marine radio telephony. A simple arrangement ofswitches enables the operator to connect either his microphone or tonefrequency generators in circuit With the modulator of the transmitter,according to requirements. The operator also has a choice of receptionon a loud speaker or ona plurality of tone frequency filters which areused under standby conditions for reception of distress signals from aremote point.

My invention will now be described in more detail, reference being madeto the accompanying drawing, in which the sole figure thereof representsmore or less conventionally certain apparatus, the elements of which arearranged in a novel combination.

Referring to the drawing, I show therein an antenna l connected to aswitch blade 2 having two positions in which contacts 3 and 4 arealternatively used.

The receiver For reception the switch 2 is set to the position shown.Incoming signal energy is, therefore, fed to the primary winding of atransformer 5. The secondary winding of transformer 5 forms theinductance of a tuned circuit, the tuning condenser of which isindicated at 6. Preferably, I provide a stage of radio frequencyamplification in the pentode discharge tube 1. This tube has its firstgrid connected to the tuned secondary of transformer 5. The otherterminal of this secondary is connected to an automatic gain controlarrangement |which will be hereinafter described.

Tube 1 employs a cathode resistor 8 which is shunted by a capacitor 9.The cathode circuit is grounded. The anode circuit is connected to asuitable direct current source indicated as +B, and current is fed tothe anode through the primary winding of a transformer l0. Screen gridpotential is obtained from the same source +B and is fed to the screengrid through resistor H. High frequency voltage components on the screenare bypassed to ground through capacitor 12.

The tuned secondary of transformer is connected to the first grid of aConverter tube |3. Local oscillations are supplied to the cathode ofthis tube by a suitable generator l4 which is conventionally indicated,since the details of design are unimportant. 'l'ne conventionalindication of the oscillator |4 shows the application of +B potential onconductor |5 and ground potential on conductor 10, oscillatory outputenergy being fed to the conductor l1. The converter tube |3 is alsopreferabiy provided with a screen grid and a suppressor grid, theconnections for which are conventional. The anode in tube |3 isconnected to the -l-B terminal through the primary winding of atransformer 18, this primary winding being tuned by means of a capacitor|9.

Output energy from the Converter tube l3 is fed across transfoimer E8 tothe input circuit of an intermediate frequency amplifier 20. Thisamplier may have any desired number of stages of amplication accordingto practical requirements.

The output circuit of the final stage in the intermediate frequencyamplifier 20 includes the primary of a transformer 2| which is tuned.This circuit also includes a voltage dropping resistor 22.

Rectification of the output from the I. F. amplifier 20 takes place inthe diode tube 23. This tube detects the audio-frequency signalcomponents for utilization in a responsive device and also furnishesgain control potentials. The A. V. C. circuit includes resistor 24,which is shunted by a capacitor 25, and resistor 26 in series withcapacitor 21. The A. V. C. control voltage appears on conductor 2B andis fed to the first grid in tube 1 and also across resistor 29 to theinput circuits of one or more stages of the I, F. amplifier 20.

Switch 30 has its movable contact connected through resistor 3| to thecathode of the reotifier tube 23. Resistor 3| is shunted by a bypasscondenser 32. When the switch 30 is s'et in the position shown, lowfrequency signal .components are applied simultaneously to the controlgrids in each of three discharge tubes 34, and 35. The circuitparameters of these tubes are arranged to provide a filtering actionsuch that each passes a predetermined audio frequency tone. These tubesare preferably of the duplex diode triode type which producerectification of the amplified energy traversing the space path of theamplifier section. The diode anodes 35 are parallel connected to a tunedcircuit 31. The main anode is connected to the +B terminal through atuned circuit 38. Tuned circuits 31 and'38 are inductively intercoupled.Cathode resistors 39 are shunted by capacitors 40. These elements aregrounded remotely from the cathodes. The input circuit for each of theamplifier sections in the tubes 33, 34, and 35 include grid leakresistors 4|. Input energy is applied to these input circuits acrosscapacitors 42.

Rectification components from the filtered output of the tubes 33, 34,and 35 are applied as 4 energizing potentials for individually Operatingrelays 43, 44, and 45.

The armatures of the relays 43, 44, and 45 are arranged to shift acontrol potential between that of ground and a more positive potentialderived from the +B source terminal. Resistors 46 and 41 serve as avoltage divider which, upon relay operation, may be connected betweenthe -|-B source terminal and ground. The junction between resistors 46and 41 is connected to the control grid in an amplifier tube 48. Thistube is normallyl blocked by maintaining its control grid at groundpotential while its cathode derives a somewhat more positive potentialfrom a junction between resistors 58 and 59 which constitute a Voltagedivider connected between +B and ground.

The circuit through the voltage divider elements 46 and 41 is groundedat both ends whenever one or more of the relays 43, 44, and 45 remain'unactuated However, in response to the simultaneous energization ofthese three relays, that is, upon reception of the predetermined audiofrequency components of the dstress signal, a circuit may be traced fromthe +B terminal successively through the armatures of the energizedrelays and thence through resistors 46 and 41 to ground. Hence, bysimultaneously actuating relays 43, 44, and 45, a positive potential isapplied to the grid in tube 48 and causes this tube to be conductive.

The anode circuit of tube 48 includes the winding of a relay 49. Thiscircuit is fed directly with +B potential through conductor 15. Thissame conductor supplies a suitable potential to the screen grid in tube48.

The closing of the armature of relay 49 against its front contactsupplies Operating potential from a battery or other source 50 forsounding an alarm bell 5|. In place of, or in addition to, the bell 5| alamp may be provided for producing a visual indication.

When switch 30 is moved to the position other than as shown, the outputfrom the rectifier tube 23 is directed across capacitor 52 and throughresistor 53 so as to control the first grid of a pentode discharge tube54. This tube amplifies the audio frequencies which may represent speechsignals and which may, therefore, be used in a responsive device such asthe loud speaker 55. The transformer 56 which is used for coupling theoutput circuit of tube 54 to the voice circuit of the loud speaker 55may, if desired, contain an additional winding 51, the terminals ofwhich may be used to transmit speech currents to one or more additionalresponsive devices, such as an earphone head set.

The transmitter In order to transmit a distress signal or to transmitspeech signals, the transmitter section vof my two-way communicationsystem may be vmary winding on transformer 61.

includes the secondary winding of a transformer v61. Tube 64 containsthe usual screen grid and beam focusing electrodes, the latter beingcarried at cathcde potential. The screen grid current is drawn throughresistor 69.

.The amplified carrier wave energy of tube 64 is modulated by couplingthe output circuit to a push-pull modulator tube 68. This tube ispreferably of the twin triode type where the cathodes are connected toground through individual cathode resistors 16, these resistors beingshunted by capacitors 1|. The anodes of tube 68 are connectedrespectively to the terminals of the pri- This Winding has a midtapwhich is fed with +B potential.

Output energy from the power amplifier tube 64 is impressed across acapacitor 12 for controlling the energy in a parallel tuned circuitconsisting of a transformer primary 13 and capacitor 14. The secondarywinding 15 of this transformer is in circuit between ground and antennacoil 16. This coil is connected to the antenna i through switch point 4and switch blade 2.

For the purpose of transmitting distress signals which are composed of atriad modulation, I preferably employ three low frequency generators 11,18, and 19. These generators are conventionally shown. A wide choice offrequencies is available for the combination of tones to be produced bythese generators. The frequencies may, therefore, be harmonicallyrelated or dissonantly related if desired. The chosen frequencies mayalso be within or without the band of frequencies occupied by speechWaves. Anode potential is supplied through conductors 80, groundpotential through conductors and the output frequency is coupled acrosscapacitors 82 to one of the stationary contacts of a switch 84. Themovable contact of this switch is connected to a control grid in atriode amplifier tube 85. 86 provides a high inductive impedance. groundconnection for the output circuits of the generators 11, 18, and 19.

Amplification of the three tone frequencies derived from the lowfrequency generators 11, 18, and 19 is obtained in the tube 85. Thistube has an output circuit connected between the +B supply and theanode, and the useful output energy traverses the primary winding of atransformer B1. The secondary of this transformer has its terminalsconnected to the control grids in the twin triode amplifier tube 68. Thecentertap on the secondary of transformer 81 is grounded. Tube 35 hasits cathode connected through a cathode resistor 88 to ground. Thisresistor is shunted by capacitor 69. A bypass condenser 90 is connectedin shunt with the +13 source, the negative terminal of which isgrounded.

For the purpose of transniitting voice signals, switch 84 is moved intoconnection with a circuit leading through the secondary winding oftransformer 9|. It is then possible to transmit sig- `nals from themicrophone 92 in place of the distress signals. A unitary control ofswitches 84 and 30 is indicated by the broken-line connectiontherebetween. This arrangement, or the use of a double-pole-double-throwswitch, is convenient, but not essential, when shifting the set fromdistress signaling to two-way telephone service, and vice versa. Themicrophone circuit which is fed through the primary winding oftransformer 9| may be energized by means of a direct current source 93.

A choke vplifier 26, and the diode rectifier 23.

Recapitulation w To those skilled in the art, the various details of thecircuit arrangements will be well understood without furtherdescription. It will also be understood that various modifications ofthe circuit details may be made without departing from the spirit of theinvention. It should be noted further that the system as herein shownand described is capable of operation under Varying conditions such asmight ordinarily be met in shipto-ship and ship-to-shore communicationwork. The operation of the system may be recapitulated as follows:

When the apparatus is to be set in a *'standby condition, the antennaswitch 2 will be positioned as shown. The antenna is then connected tothe receiver and any incoming signals such as a distress signal will befed to the heterodyne receiving apparatus comprising the radio frequencyamplifier stage 1, the Converter stage |3, the I. F. am- I-Ieterodyningof the incorning signals with output from local oscillator 14 isobtained in the converter tube stage |3. The I. F. frequency componentof the incoming signal is then amplified in the I. F. amplifier 20 andrectification takes place in tube 23. Automatic gain control potentialsare fed back through conductor 28 to the input circuits of one or morestages including those of the R. F. amplifier and of the I. F.amplifier.

The output energy from the detector stage 23 is also used by feeding thesame through switch 30 when in the position shown so as to control thethree filter tubes 33, 34, and 35. If a distress signal having thedesignated low frequency components is received, these filter amplifiersWill all be controlled simultaneously so as to energize their associatedrelays 43, 44, and 45.

The simultaneous actuation of the relays which respond to the distresssignal causes the amplifier tube 48 to be controlled and to pass currentwhich energizes relay 49. Closing of the contacts of this relay actuatesthe alarm device 5|.

After receiving the distress signal, the operator may move the switch 30into the other position for reception of voice signals on the loudspeaker.

If the transmitter is to be used either for sending out a distresssignal or for communication by means of voice signals, switch 2 will bemoved into position for connecting the output of the transmitter to theantenna l.

Assuming that a distress signal is first to be transmitted, switch 84will be positioned as shown. The three tone frequencies of thegenerators 11, 18, and 19 will be combined as control modulations foramplification in the tube stage 85 and for subsequent amplification inthe twin triode tube 68. The power amplifier tube is fed with energyfrom the oscillator 60 by virtue of the coupling of its control grid tothe output side of the oscillator 60 across capacitor 66. Thetransformer 61 applies modulation potentials to the output circuit oftube 64. Anode potential Variations are reflected in the transfer ofoutput energy across capacitor 12 to the antenna circuit.

As previously stated, the transmission of voice is novel and providesimproved facillties for distress signaling and for two-way communicationwork.

I claim:

1. In a distress signaling system, a radio receiver including a localoscillator and means for heterodyning its .output with incoming radiosignals, an intermediate frequency amplifier and detector connected incascade relation to said heterodyning means, separate means foramplifying and filter-passing individual tones in a mixture of at leastthree low frequency components of the output from saiddetector, aplurality of individual relays each operable by amplified currentsderived from a different one of said separate means, and an alarm devicecperable only upon the simultaneous operation of all of said relays.

2. In radio apparatus for distress signaling, wherein a transmitter anda receiver are provided, the improvement which provides a combinationwith said transmitter of a plurality of audio-fresuency generators eachtuned to a different frequency and all simultaneously connectable to themodulator section of said transmitter, whereby an outgoing distresssignal may be characterized as a mixture of at least three predeterminedand substantially equal-amplitude tone modulations of the carrier waveof said transmitter, and the combination with said receiver of aplurality of selective filter units for simultaneously passing each ofthe several predetermined audio frequencies of which said distresssignal is composed, and, further, an alarm device including time delaymeans and an operating circuit closeable only in response to thereception of a distress signal which possesses the full complement ofsaid predetermined audio frequency components and is suficientlyprolonged to outlast the operation of said time delay means.

3. In a selector for detecting the presence of certain low frequencycomponents in a distress signal, a plurality of electronicamplier-filter circuits each tuned to a respective one of said lowfrequency components, relays each energizable by output from arespective one of said amplifier-filter circuits, each relay having anarmature movable between front and back contacts, an electronic devicehaving input and output circuits, time delay elements in said inputcircuit, means whereby a cut-off bias is applied to said input circuitso long as any one of said relay armatures remains engaged with its backcontact, means for causing said electronic device to become conductiveafter a predetermined delay following a circuit closure through all ofsaid relay armatures and their front contacts in series, and an alarmdevice operable in response to the development of a conductive state insaid electronic device.

4. The method of detecting the presence of a plurality of predeterminedlow frequency components in a distress signal with the aid of anelectron discharge tube circuit arrangement which is subject to controlby the mutual cooperation between a plurality .of relays correspondingto the several low frequency components of said distress signal, saidmethod comprising filter-passing each of said predetermined lowfrequency components, removing a blocking bias from the dischai'ge tubeof said circuit arrange- 0 ment which is normally maintained by any one7 of said relays when unenergized, and producing a delayed response insaid discharge tube by rendering the same conductive after closure of aconductive path for an unblocking potential to be applied to saiddischarge tube, said path having series connections which areindividually controllable by each of said relays.

5. In a distress signaling system, a radio transmitter including acarrier wave source, means for modulating said source by a wave which isconstituted as a mixture of output energies from at least threeparallel-connected and simultaneously opera-tive generators, eachdeveloping a different `low frequency, means for amplifying andradia-ting the carrier wave energy so modulated, a heterodyne receiverincluding means for demod- -ulating and detecting said carrier waveenergy, frequency-selective means subject to control by the detectedoutput energy from said receiver for completing a circuit through asmany points of rcircuit closure as the number of low frequencycomponents in said detected output, said frequency selective means beingcapable of accepting substantially the same frequencies as those of saidlow frequency generators and no others, and an alarm device operable inresponse to the completion of said circuit.

6. In a distress signaling system, a radio receiver for activating analarm device only in response to a modulated carrier wave themodulations of which are constituted as a mixture of at least three lowfrequency components of substantially equal amplitude, frequencyselective filters for passing said frequency components after detection,a plurality of electronic devices each having the winding of a relay inits load circuit and each device being subject to control by rectifiedenergy from a respective one of said filters, an alarm device having anelectronic switch for Operating the same, and relay contact means forcontrolling said switch, said means in- .cluding series-connected pointsof circuit closure, each circuit closure point being controllable by arespective one of said relays, whereby said alarm device is caused to beactuated only when the full complement of said low frequency componentsis detected.

7. Apparatus according to claim 6 in combination with normally closedcontacts on said relays, and circuit means extending through saidcontacts for applying a cut-off bias to the electron discharge device ofsaid electronic switch.

IRVING F. BYRNES.

REFERENCES CITED The following references are of record in the file yofthis patent:

UNITED STATES PATENTS Number Name Date 2,052 ,581 Richards Sept. 1, 19362,148,578 Pullis Feb. 28, 1939 2,325,829 Boswau Aug, 3, 1943 1,932,232Seeley Oct. 24, 1933 2,131,042 Halstead Sept. 27, 1938 2,203,871 KochJune 11, 1940 2,3%,618 Koch Mar. 21, 1944 2,198,901 Boswau Apr. 30, 19402,289,'794 Martin July 14, 1942 2,368,953 Walsh Feb. 6, 1945 FOREIGNPATENTS Number Country Date 191,096 Switzerland Aug. 16. 1937

